Semiconductor memory card access apparatus, a computer-readable recording medium, an initialization method, and a semiconductor memory card

ABSTRACT

A predetermined number of erasable blocks positioned at a start of a volume area in a semiconductor memory card are provided so as to include volume management information. A user area following the volume management information includes a plurality of clusters. A data length NOM of an area from a master boot record &amp; partition table sector to a partition boot sector is determined so that the plurality of clusters in the user area are not arranged so as to straddle erasable block boundaries. Since cluster boundaries and erasable block boundaries in the user area are aligned, there is no need to perform wasteful processing in which two erasable blocks are erased to rewrite one cluster.

This application is a divisional application of U.S. patent applicationSer. No. 10/444,966, filed May 27, 2003, which is a divisionalapplication of U.S. patent application Ser. No. 09/691,269, filed Oct.19, 2000.

This application is based on an application No. 11-299636 filed inJapan, the content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an access apparatus for accessing asemiconductor memory card having internal nonvolatile memory such asEEPROM (electrical erasable programmable read-only memory), acomputer-readable recording medium for recording an initializationprogram for a semiconductor memory card, an initialization method, and asemiconductor memory card, and in particular to an improvement forraising the efficiency with which data can be rewritten in thenonvolatile memory.

2. Description of the Background Art

Semiconductor memory cards have the advantage of being small andlightweight, and are well on the way to consolidating their position asthe recording medium of choice in a wide variety of technical fields. Asemiconductor memory card has an internalized nonvolatile memory knownas EEPROM, which is accessed by a connected device, enabling thesemiconductor memory card to be used as a recording medium. Data can bedirectly written into blank EEPROM sectors in the same way as formagnetic or optical discs. However, when EEPROM sectors already containdata, this data has to be deleted, returning the sectors to a blankstate, before new data can be written into the sectors. In the type ofEEPROM known as NAND (Not And) used in many semiconductor memory cards,the operation for returning sectors to a blank state has to be performedon 32 sectors at one time (in this nonvolatile memory, a group of 32sectors is known as an erasable block). Consequently, the semiconductormemory card contains a specialized internal control circuit forrealizing memory management using erasable blocks as access units.Status control of erasable blocks, and reading and writing of datato/from erasable blocks, is managed by this control circuit.

This means that the semiconductor memory card has a unique hardwarestructure (physical layer) that is completely different from that usedin magnetic and optical discs. However, a layer model shown in FIG. 1Ais formed from physical, file system, and application layers in the sameway as in a magnetic or optical disc. FIG. 1B shows a detailed layout ofthe physical layer. In the drawing, the physical layer includes a volumearea in which a plurality of erasable blocks are arranged. Each erasableblock is formed from 32 sectors and has a data length of 16 KB. Thelayout of the file system layer shown in FIG. 1C is what is commonlyknown as a FAT (file allocation table) file system. In a FAT filesystem, management of the volume area is performed in units known asclusters. Volume management information is arranged at the start of thevolume area, and a user area for recording user data is arrangeddirectly following the volume management information. The volumemanagement information includes a master boot record, a partition table,a partition boot sector, a duplexed file allocation table (FAT), and aroot directory entry. The duplexed FAT shows links between the pluralityof clusters included in the volume area. This kind of file system layerenables data to be stored in the application layer in a hierarchicalstructure formed from directories and files. By installing a layermodel, the access apparatus can access a semiconductor memory card withthe same procedure used to access a recording medium, such as a magneticor optical disc, without the need to pay attention to differences in thephysical layer.

However, a user has many opportunities to determine the data size of thevolume area when data is stored in the volume area of the file system.When the size of the volume area is changed in response to a userrequest, the number of clusters included in the volume area increases ordecreases accordingly. If the number of clusters is increased ordecreased, the FAT formed from entries corresponding to these clustersalso increases or decreases, respectively, as does the size of thevolume management information in which the FAT is included. If the sizeof the volume management information is increased or decreased, a startaddress of the user area following the volume management informationwill also be changed. The start address of the user area changesaccording to the size of the volume area. Consequently, the startaddresses of each cluster also change according to the size of the userarea.

If the start address of each cluster changes according to the size ofthe user area, clusters may straddle the boundaries between two erasableblocks, and the end portion of the volume management information may bearranged in the same erasable block as a cluster positioned at the startof the user area. FIG. 1D shows the layout of the volume area when theend portion of the volume management information and the clusterpositioned at the start of the user area are in the same erasable block.If clusters are arranged as shown in the drawing, and a user desires tomodify data stored in a particular cluster, the two erasable blocks inwhich the cluster is arranged have to be read and then returned to ablank state. However, nonvolatile memory is formed from a memorycomponent that includes a floating gate buried in an insulating layer.This memory component can only be erased a few tens of thousands oftimes, so if the phenomenon in which two erasable blocks have to beerased to modify one cluster frequently occurs, the lifespan of thenonvolatile memory will be significantly reduced.

Generally speaking, when 32 sectors are managed as one cluster, writingdata into a cluster can be completed in 32×200 μs (200 μs is the timerequired to write each sector), provided that the write destination hasalready been erased. However, if the write destination has to be erasedbefore data can be written, a 2 ms erasure period is added. If thecluster straddles the boundary between two erasable blocks, both blocksneed to be erased, and erasing the write destination takes 4 ms. As aresult, the time required to write data is significantly lengthened.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an access apparatusthat achieves a reduction in the processing time required to modifyerasable blocks, as well as forming a data storage format in asemiconductor memory card that enables a nonvolatile memory having alonger lifespan to be realized.

The type of semiconductor memory card known as a secure digital (SD)memory card has made great strides toward resolving the aforementionedproblems of reduction in processing time and nonvolatile memorylongevity for the following reasons. In an SD memory card, an area knownas the protected area, which cannot be used by the general user, isprovided. This protected area is used to store secret information, suchas an encryption key used for encrypting data, billing information usedto bill a user when a copyrighted material is reproduced, and the like.The amount of data which needs to be kept secret varies according to thetype of application program used, so that the size of the protected areahas to change according to the type of application program. If the sizeof the protected area is changed, this means that the layout of thevolume area also changes in response to the type of application program.If the layout of the volume area changes in this way, a layout in whichclusters straddle the boundaries between erasable blocks is oftengenerated, so achievement of the above-mentioned object is particularlydesirable.

In order to achieve the above-mentioned object, the semiconductor memorycard access apparatus may have the following structure. The accessapparatus performs file access on a semiconductor memory card that has amemory area comprising a plurality of sectors by managing data in eachgroup of 2^(j) sectors (j being 0 or a positive integer) as a cluster,and managing one or more clusters as a file. Here, each group of 2^(i)consecutive sectors in the memory area forms a block (i being 0 or apositive integer), which is the smallest unit on which data erasure canbe performed. The access apparatus includes a calculation unit, areserving unit, and a recording unit. The calculation unit calculates asize of volume management information based on a number of clusters inthe memory area that are to be managed. Here, the volume managementinformation includes a file allocation table that indicates, for eachfile, links between clusters corresponding to the file. The reservingunit reserves a first area for recording the volume managementinformation, and a second area for recording user data. The first areahas a data size larger than the calculated volume managementinformation, and is formed from m×2^(j) sectors (m being a positiveinteger), while the second area is formed from sectors following thefirst area. The recording unit records volume management information inthe first area, and user data in the second area, and manages the volumemanagement information and the user data as clusters. In this accessapparatus, an area in the volume area having m clusters (m is a positiveinteger) is reserved for recording volume management information, sothere is no possibility of any cluster being stored straddling twoerasable blocks. Cluster boundaries can be aligned with erasable blockboundaries, and the boundary of the volume management information can bealigned with an erasable block boundary. Consequently, only one erasableblock needs to be erased when a cluster is rewritten or overwritten, andthe number of times that erasable blocks have to be erased can bereduced. If the number of block erasures is reduced, the semiconductormemory card can write data in a shorter time, and the lifespan of thenonvolatile memory itself can be increased.

Here, the volume management information may include in addition to thefile allocation table, a master boot record, a partition table,partition boot sector information, and a root directory entry.Furthermore, the recording unit records the master boot record and thepartition table in a first sector of the first area, skips apredetermined number of sectors and then records the partition bootsector information, the file allocation table, and the root directoryentry in subsequent sectors. As a result, an end of the first area canbe aligned with an end of the root directory entry. The number ofsectors between the master boot record showing the start of the drive,and the partition boot sector showing the front of the partition area,can be adjusted, so the volume management information can be restrictedto a first area formed from m clusters, and compatibility with devicesthat use a FAT file system preserved.

Here, the calculation unit may calculate a sum SUM by totaling a numberof sectors used to record the partition boot sector information, thefile allocation table, and the root directory entry. The reserving unitreserves the first area by calculating the value of m based on an{equation 1} NOM+SUM=2^(j)×m. Here, NOM is a number of sectors. Therecording unit calculates the predetermined number of sectors bysubtracting 1 from the number of sectors NOM. Even if the size of thefile allocation table changes, a first area which is larger than thesize of the volume management information and is an integral multiple oferasable block size is reserved. As a result, a necessary minimum sizefor the first area can be reserved, no matter how the size of the fileallocation table is calculated.

Here, the recording unit may set the predetermined number of sectors inthe partition table recording the volume management information. In thisstructure, even if the size of the first area changes, causing the startaddress of the second area to change, a number of sectors, obtained bysubtracting 1 from the number of sectors NOM, is set in the partitiontable, so the access apparatus can access the user area accurately byreferring to the partition table.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings which illustrate a specificembodiment of the invention. In the drawings:

FIG. 1A shows a layout model formed from a physical layer, a file systemlayer compliant with ISO/IEC9293, and an application layer;

FIGS. 1B and 1C show the format of the physical layer and the filesystem layer;

FIG. 1D shows a layout of the volume area when an end portion of thevolume management information and a cluster positioned at the start ofthe user area are arranged in the same erasable block;

FIG. 2A is an external view of an semiconductor memory card;

FIGS. 2B and 2C are external views of access apparatuses;

FIG. 3A shows an internal structure of a semiconductor memory card andan access apparatus;

FIG. 3B shows a layer model for software used by the access apparatus;

FIG. 4 shows a data storage format, compliant with the ISO/IEC9293standard, used by a nonvolatile memory 1;

FIG. 5 shows a structure of a partition control area, a system area, anda user area included in the volume area;

FIG. 6A illustrates a structure of a master boot record and a partitiontable sector;

FIG. 6B shows a structure of a partition boot sector;

FIG. 7A shows a structure of a duplexed FAT;

FIG. 7B shows a structure of a root directory entry;

FIG. 7C shows a structure of the user area;

FIG. 8 shows an example of a file storage method;

FIG. 9 shows an example of settings for the root directory entry and theFAT when a file AOB001.SA1 is stored in a plurality of clusters;

FIG. 10A shows the relationship between erasable blocks and clusters;

FIG. 10B shows clusters when n=1;

FIG. 10C shows clusters when n=16;

FIG. 11A envisages a situation when m clusters out of s erasable blocksare allocated for recording of volume management information;

FIG. 11B shows the number of clusters allocated for recording of volumemanagement information when n=1;

FIG. 11C shows the number of clusters allocated for recording of volumemanagement information when n=16;

FIG. 12 is a drawing obtained by constructing the partition controlarea, the system area and the clusters with a size calculated usingequations 11 and 12;

FIG. 13 is a flowchart showing an initialization procedure for thevolume area;

FIG. 14 shows a structure of an access apparatus and a semiconductormemory card in a second embodiment;

FIG. 15 shows an internal structure of a secure processing unit 11;

FIG. 16 shows a detailed structure of a volume area provided with aprotected area;

FIG. 17 shows an example layout for the user data area;

FIG. 18 shows an example layout for the protected area;

FIG. 19 shows an internal structure of an access control unit 2 in athird embodiment;

FIGS. 20A to 20D show a processing sequence performed when rewriting anerasable block;

FIG. 21 shows an internal structure of a file system operation unit 9 inthe third embodiment;

FIG. 22 is a flowchart showing detailed processing performed by the filesystem operation unit 9 in the third embodiment;

FIGS. 23A and 23B show an erasing process performed on an erasable blockin the third embodiment;

FIG. 24 shows an internal structure of an access control unit 2 in afourth embodiment;

FIG. 25 is a flowchart showing detailed processing performed by the filesystem operation unit 9 in the fourth embodiment;

FIGS. 26A and 26B show an erasing process performed on an erasable blockin the fourth embodiment;

FIGS. 27A and 27B show the relationship of cause-and-effect betweenfragmentation and overheads when a command is issued;

FIG. 28 is a flowchart showing a detailed processing sequence forfragmentation elimination processing performed on a logical address;

FIGS. 29A to 29D show models envisaged for each of variables s, t, u, v,and y shown in the flowchart of FIG. 28;

FIGS. 30A to 30C shows how fragmentation is eliminated in a fifthembodiment;

FIG. 31 shows a new extended attribute specified using an implementationuse extended attribute in UDF;

FIG. 32 shows an internal structure of a semiconductor memory cardprovided with a backup area;

FIG. 33 shows an internal structure of a semiconductor memory card in asixth embodiment; and

FIGS. 34A to 34C show content of processing performed by a file systemoperation unit 9 in a seventh embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of embodiments of a semiconductor memorycard, and of a system including a semiconductor memory card and anaccess apparatus, with reference to the drawings.

FIG. 2A shows an external view of a semiconductor memory card 100, andFIGS. 2B and 2C show external views of access apparatuses. FIG. 3A showsan internal structure of the semiconductor memory card 100 and an accessapparatus 200.

The semiconductor memory card 100 has the external structure of FIG. 2A,being 32.0 mm long, 24.0 mm wide, and 2.1 mm thick: about the size of apostage stamp, and small enough for a user to hold on the tip of onefinger. The semiconductor memory card 100 has nine connectors forconnecting to an access apparatus 200, and a write protect switch 101 onone side, which can be set by the user to permit or prohibit overwritingof recorded data. As shown in the lower part of FIG. 3A, thesemiconductor memory card 100 includes a nonvolatile memory 1 formedfrom NAND EEPROM, an access control unit 2, and a work memory 3. Theaccess control unit 2 writes data into the nonvolatile memory 1, readsdata from the nonvolatile memory 1, and erases data, according tocommands issued by the access apparatus 200. The work memory 3 is usedfor temporary data storage when data read from the nonvolatile memory isrewritten or written back into the nonvolatile memory.

Next, an access apparatus 200, such as a domestic sound system shown inFIG. 2B or an information processing apparatus such as a personalcomputer shown in FIG. 2C, is described. Such an access apparatus 200includes a card connector 4, a secondary memory 5, a CPU 6, and aprimary memory 7. The card connector 4 is used to connect to thesemiconductor memory card 100. The secondary memory 5 stores varioustypes of software for accessing the semiconductor memory card 100. TheCPU 6 performs overall control of the access apparatus 200. The primarymemory 7 is used for temporary storage of the FAT and the root directoryentry when the semiconductor memory card 100 is accessed. FIG. 3B showsa layout model for software used in the access apparatus 200. In thedrawing, the access apparatus software includes an application program8, a file system operation unit 9, and a device driver 10. Theapplication program 8 performs predetermined processing, such as audioand video reproduction, for the access apparatus 200. The file systemoperation unit 9 executes file reading, writing, erasing and modifying(rewriting) operations on the file system, according to instructionsfrom the application program 8. The device driver 10 performs operationson the file system by issuing read and write commands to thesemiconductor memory card 100.

The following is an explanation of an example data storage format forthe nonvolatile memory 1. The nonvolatile memory 1 performs data storageusing the format shown in FIG. 4. In the drawing, the entire nonvolatilememory 1 is referred to as the volume area. The volume area is manageddivided up into a plurality of clusters, and includes a partitioncontrol area and a partition (also known as the regular area). Thepartition is divided into a system area and a user area, as shown on theright-hand side of FIG. 4.

A start address of the user area follows directly after the system area.However, the size of the duplexed FAT in the system area variesaccording to the size of the user area, so that the start address of theuser area changes accordingly, as was explained in the Background Artsection. Each sector in the volume area is indicated by a physicaladdress relative to the start of the volume area.

Next, each of the areas included in the volume area is described inturn. FIG. 5 shows a structure for the partition control area, thesystem area, and the user area included in the volume area.

The partition control area includes a master boot record & partitiontable sector, and reserved information 1/2, and 2/2. FIG. 6A shows adetailed structure of the master boot record & partition table sector.In the drawing, the content of the master boot record & partition tablesector is shown hierarchically between a pair of arrows ky1. The masterboot record & partition table sector includes a master boot record, fourpartition tables 1, 2, 3, and 4, and a signature word.

The master boot record is a sign indicating to the access apparatus 200that a subsequent area is physically one medium (one physical medium).In FIG. 6A, the volume area has only one master boot record, so thevolume area is recognized by the access apparatus 200 to be one physicalmedium. Generally, if two master boot records are arranged in the volumearea, two physical media are recognized by the access apparatus 200.

The partition table is a table recording partition information. As shownby the arrows ky2, when the semiconductor memory card 100 is used as astarter drive, the partition table includes the following fields: ‘bootindicator’, ‘starting head’, ‘starting sector/starting cylinder’,‘system ID’, ‘ending head’, ‘ending sector/ending cylinder’, ‘relativesector’, and ‘total sector’. The ‘boot indicator’ field is set at‘0x80’. The ‘starting head’ field specifies the starting head of apartition. The ‘starting sector/starting cylinder’ field specifies thestarting sector and starting cylinder of the partition. The ‘system ID’specifies a file system type, by being set at ‘01’ when the partitionsize is less than 32680 bytes, and at ‘04’ when the partition size isless than 65536. The ‘ending sector/ending cylinder’ field specifies theending sector and ending cylinder of the partition. The ‘relativesector’ field specifies the number of sectors existing before thestarting sector of the partition. The ‘total sector’ field specifies thenumber of sectors in the partition.

The following is an explanation of the partition in the semiconductormemory card 100. The partition is formed from the system area, followedby the user area, but this explanation begins with a description of theuser area, with reference to FIG. 7C.

The user area stores files in units no smaller than a cluster. The arrowff2 drawn using a broken line in FIG. 7C shows the plurality of clusters002, 003, 004, 005 . . . included in the user area. The numbers 002,003, 004, 005, 006, 007, 008 . . . used in FIG. 7C are three-digithexadecimal cluster numbers that are exclusively assigned to identifyeach cluster. Since the smallest unit by which access can be performedis one cluster, storage positions within the user area are indicatedusing cluster numbers.

The system area includes a partition boot sector, a duplexed fileallocation table, and a root directory entry. The partition boot sector,the duplexed FAT and the root directory entry are described in turn,with reference respectively to FIGS. 6B, 7A and 7B.

An extended FDC (floppy disc controller) descriptor with the informationfields shown in FIG. 6B is set in the partition boot sector. The extendFDC descriptor includes the following fields: ‘jump command’, ‘creatingsystem identifier’, ‘sector size’, ‘sectors per cluster’, ‘reservedsector count’, ‘number of FATs’ (number of FATs included in the duplexedFAT), ‘number of root directory entries’ (data length of the rootdirectory entry), ‘total sectors’, ‘medium identifier’, ‘sectors perFAT’, ‘sectors per track’, ‘number of sides’, ‘number of hiddensectors’, ‘total sectors’ (the total number of sectors in the systemarea and the user area), ‘physical disk numbers’, ‘extended boot recordsignature’, ‘volume ID number’, ‘volume label’, ‘file system type’, and‘signature word’.

The duplexed FAT is formed from two FATs compliant with the ISO/IEC(International Organization for Standardization/InternationalElectroteachnical Commission) 9293 standard. Each FAT includes aplurality of FAT entries each linked to a cluster. FAT entries indicatewhether a corresponding cluster is in use or not, being set at ‘0’ ifthe cluster is not in use, and with the corresponding cluster number ifthe cluster is in use. The cluster number indicates a link to a nextcluster that should be read following this cluster. The arrow ff1 drawnusing a broken line in FIG. 7A shows a plurality of FAT entries 002,003, 004, 005 . . . included in the FAT. The numerical values ‘002, 003,004, 005 . . . ’ attached to each FAT entry show the cluster number ofthe corresponding cluster.

The root directory entry includes a plurality of file entries for aplurality of files present in the root directory. Each file entryincludes a ‘filename’ of an existing file, a ‘file identifier’, a‘number of first cluster in file’ stored at the start of the file, a‘file attribute’, a ‘recording time’ and a ‘recording date’ indicatingwhen the file was recorded, and a ‘file length’.

The following describes the file storage method by showing how a filenamed ‘AOB001.SA1’ is stored in the root directory, with reference toFIG. 8. Since the smallest unit by which the user area can be accessedis one cluster, the file ‘AOB001.SA1’ needs to be stored in the dataregion in sections that are no smaller than one cluster. The file‘AOB001.SA1’ is therefore stored having first been divided intoclusters. In FIG. 8, the file ‘AOB001.SA1’ is divided into five sectionsin keeping with the cluster size, and the resulting sections are storedinto the clusters numbered 003, 004, 005, 00A, and 00C.

FIG. 9 shows one example of how the root directory entry and FAT need tobe set when the file ‘AOB001.SA1’ is stored having been divided up intosections and stored. In the drawing, the start of the file ‘AOB001.SA1’is stored in cluster 003, so that cluster number 003 is written into‘the number of first cluster in file’ in the root directory entry toindicate the cluster storing the first section of the file. Thesubsequent sections of the file ‘AOB001.SA1’ are stored in clusters 004and 005. As a result, while the FAT entry 003 (004) corresponds tocluster 003 that stores the first section of the file ‘AOB001.SA1’, thisentry indicates cluster 004 as the cluster storing the next section ofthe file ‘AOB001.SA1’. In the same way, while the FAT entries 004 (005)and 005 (00A) respectively correspond to clusters 004 and 005 that storethe next sections of the file ‘AOB001.SA1’, these entries respectivelyindicate cluster 005 and cluster 00A as the clusters storing the nextsections of the file ‘AOB001.SA1’. By reading the clusters with thecluster numbers written into these FAT entries in order as shown by thearrows fk1, fk2, fk3, fk4, fk5 . . . in FIG. 9, all of the sectionsproduced by dividing the file ‘AOB001.SA1’ can be read. As explainedabove, the user area of the semiconductor memory card 100 is accessed inunits of clusters, each of which is associated with a FAT entry. Notethat the FAT entry that corresponds to the cluster storing the finalsection of an AOB file (the cluster 00C in the example shown in FIG. 9)is set with the cluster number ‘FFF’ to show that the correspondingcluster stores the final section of a file.

The above explanation gave a brief overview of the file system in thenonvolatile memory 1 of the present invention. The following explanationconcentrates on the principle objective of the embodiments, describinghow cluster boundaries and erasable block boundaries are aligned, inother words how the boundary of the system area and the user area isaligned with a boundary between two erasable blocks. The embodimentsexecute two improvements in order to realize this boundary alignment.The first of these involves setting cluster size at 1/nth the size oferasable block size (n being 1, 2, 4, 8, 16, or 32). FIG. 10A shows therelationship between erasable blocks and clusters. Here, a cluster isspecified to be 1/n of the size of an erasable block, that is 1/n of 16KB (1/n of 32 sectors). FIG. 10B shows a number of clusters when n=1,and FIG. 10C a number of clusters when n=16.

The second improvement involves allocating an area in the volume area,having a size m times the size of a cluster, for recording the volumemanagement information. FIG. 11A envisages a situation when m clustersfrom among s·n clusters included in s erasable blocks are allocated forrecording the volume management information. If m clusters are allocatedfor recording the volume management information, an area m/n inside thes erasable blocks will be occupied by the volume management information,and the remaining (s·n−m)/n area will be allocated to the user area.

By setting the size of the volume management information at m timescluster size, the volume management information and s·n−m clusters canbe compressed so that clusters do not straddle the boundaries betweentwo erasable blocks.

FIG. 11B shows the number of clusters allocated to the volume managementinformation when n=1, and FIG. 11C shows the number of clustersallocated to the volume management information when n=16. As thesedrawings clearly show, a plurality of clusters are fitted precisely intoa plurality of erasable blocks by setting the volume managementinformation, so that no clusters straddle the boundaries betweenerasable blocks. A detailed layout of a volume area whose size has beenadjusted in this way is shown in FIG. 5. In the drawing, the size of thepartition control area is NOM, the size of the partition boot sector isRSC, the size of the duplexed FAT is Size 1×2, the size of the rootdirectory entry is RDE, the total sector size is TS, and the number ofsectors included in a cluster SC.

In FIG. 5, a Size 1 of the FATs included in the duplexed FAT, isdetermined according to total sector size TS. More specifically, it is avalue calculated using an equation 11 described hereafter.For FAT12: Size 1=(((((TS−(RSC+RDE))/SC)+2)×12/8)+511)/512For FAT16: Size 1=(((((TS−(RSC+RDE))/SC)+2)×16/8)+511)/512  Equation 11

Here, FAT12 indicates a file system in which each FAT entry is allocated12 bits, and FAT16 a file system in which each FAT entry is allocated 16bits.

In equation 11, (TS−(RSC+RDE)) is the number of clusters required forthe recording performed by the user area. The indicator number 2 isadded to this number, the resulting value then being multiplied by thebyte length of the FAT entry (12 or 16), and then divided by 8 to obtainthe FAT byte length. An offset value of 511 bytes is added to the resultof this calculation, and the resulting figure divided by a sector bytelength of 512 to calculate the number of sectors required to store oneFAT. If the FAT data length were to be 1 byte, dividing the FAT data by521 would result in the number of sectors in the FAT being calculated as0. However, addition of the offset value 511 by equation 11 ensures thata Size 1 having at least one sector will be calculated.

One important point to note in FIG. 5 is the size of the partitioncontrol area, known as NOM. The NOM is set at a value ‘SC+α’ to ensurethat the partition control area and the system area belong to differentclusters. The reason for setting the NOM in this way is to preventfailures to modify clusters in the system area from having a knock-oneffect on the partition control area. In other words, if the master bootrecord & the partition table sector in the partition area are damaged bysuch a modify failure, the semiconductor memory card 100 will no longerbe recognized as an authorized recording medium by the access apparatus200. The NOM is set at SC+α, in order to avoid such a worse-casescenario.

The value SC+α is set in the following way. Value α is calculated bydividing (RSC+RDE+Size 1×2) by SC so that the sum of RSC, Size 1×2, andRDE is an integral multiple of SC, and subtracting the remainder of thiscalculation from SC. If these facts are taken into account, the NOM iscalculated as in equation 12.NOM=(SC−(RSC+RDE+Size 1×2)% SC)+SC  Equation 12

If α is specified in this way, the partition control area and the userarea will be formed so as to fit exactly into a plurality of erasableblocks, and the boundary between the system area and the user area willbe aligned with the boundary of erasable blocks. If such alignment ofboundaries can be realized, the boundaries of all subsequent clusterswill be aligned with boundaries of erasable blocks.

Here, an example, showing how the NOM and Size 1 are calculated when theSC is 32 sectors (16 KB), the RDE is 32 sectors, the RSC is 1 sector,and the TS is 65600 sectors, is described. If the type of the duplexedFAT is FAT12, Size 1 is calculated in the following way using equation11.Size    1 = (((((TS − (RSC + RDE))/SC) + 2) × 12/8) + 511)/512   = (((((65600 − (1 + 32))/SC) + 2) × 12/8) + 511)/512   = 7  sectors.  

Furthermore, the NOM is calculated in the following way using equation12.NOM = (SC − (RSC + RDE + Size  1 × 2)  %  SC) + SC   = (32 − (1 + 32 + 7 × 2)%  32) + 32   = 47    sectors.

FIG. 12 illustrates a partition control area, a system area, andclusters, according to the calculated sizes. The master boot record &partition table sector, and the reserved information 1/2 are arranged insectors PSN000 to PSN031, and the reserved information 2/2, thepartition boot sector, and the duplexed FAT are arranged in sectorsPSN032 to PSN063. The root directory entry is arranged in sectors PSN064to PSN095. In the volume area, 32 sectors form one erasable block, sothe master boot record, the partition table, and the reservedinformation 1/2 are arranged in a first erasable block 001, the reservedinformation 2/2, the partition boot sector, and the duplexed FAT arearranged in a second erasable block 002, and the root directory entry isarranged in a third erasable block 003. The root directory entry isstored in a same-sized erasable block, so that the boundary between theuser area and the system area matches a boundary between erasableblocks.

The above volume area layout is realized when the file system operationunit 9 performs initialization on the nonvolatile memory 1. Theprocedure for performing this initialization processing is explainedwith reference to the flowchart of FIG. 13.

At step S1, the file system operation unit 9 determines cluster size inaccordance with a size of the area to be formatted (TS) and a totalstorage capacity of the semiconductor memory card 100, a operationsystem operated by the access apparatus 200, and instructions from auser.

Once cluster size has been determined, at step S2, the file systemoperation unit 9 uses cluster size SC and the total sector size TS todetermine whether a FAT12 or a FAT16 file system should be used. Onceone of a FAT12 and FAT16 file system has been determined, at step S3 thefile system operation unit 9 determines the length RDE of the rootdirectory entry (in these embodiments the RDE is fixed at 32 sectors),and following this, in step S4, determines the length RSC of thepartition boot sector (in these embodiments the RSC is fixed at 1sector). Once the RDE and the RSC have been obtained, the file systemoperation unit 9 uses the equation 11 to calculate the data length ofthe FAT, at step S5. Then, at step S6, the file system operation unit 9uses the equation 12 to calculate the NOM so that the master boot recordand the partition boot sector are in different clusters.

The processing performed in the above steps S5 to S7 is virtuallyidentical to that performed in the previously described equations 11 and12. However, the processing performed in steps S7 to S9 is firstintroduced in this flowchart. At step S7, the file system operation unit9 calculates a number of clusters CN in the user area using a equation13.CN=(TS−(RSC+RDE+Size 1×2+NOM))/SC  Equation 13

At step S8, the file system operation unit 9 calculates the data lengthof the FAT using the following equation 14.For FAT12: Size 2=(((CN+2)×12/8+511)/512For FAT16: Size 2=(((CN+2)×16/8+511)/512  Equation 14

At step S9, the file system operation unit 9 compares the Size 1calculated at Step S5, and the Size 2 calculated at Step S8, and if thetwo values are identical, ends processing. If the values are notidentical, the file system operation unit 9 substitutes Size 1 for Size2 at step S10, moves to step S6, and recalculates the NOM. Since Size 1is now a different value due to the substitution, a different NOM can becalculated by moving to step S6. Then, the file system operation unit 9recalculates Size 2 at step S8, based on the newly calculated NOM, andif Size 1 and Size 2 are identical, step S9 is Yes, and processing ends.

The NOM calculated using the above processing is set in the ‘relativesector’ field in the partition table showing the number of sectorsexisting before the starting sector of the partition, and the TS is setin the ‘total sector’ field in the partition table.

The SC is set in the ‘sectors per cluster’ field in the partition bootsector, showing the number of sectors in each cluster. Furthermore, theRDE, showing a number of sectors, is multiplied by the sector length of512 bytes, and then divided by 32 to obtain a number of file entries,this number then being set in the ‘number of root directory entries’field in the partition boot sector. The Size 1 is set in the ‘sectorsper FAT’ field showing the number of sectors in each FAT, in thepartition boot sector. The access apparatus 200 refers to these valuesset in the partition table and the partition boot sector when specifyingthe locations of the duplexed FAT, the root directory entry, and theuser area.

This concludes the explanation of the flowchart in FIG. 13. Next, anexample calculation illustrating how the size of the partition area andthe system area are calculated when the TS is 65568 is described.

Since the TS is 65568, at step S1 the file system operation unit 9determines the cluster size to be 32 sectors. Once the cluster size hasbeen determined to be 32 sectors, at step S2, the file system operationunit 9 determines that a FAT12 file system should be used by referringto the cluster size SC and the total sector size TS. In theseembodiments, the size of the RDE and the RSC are fixed at 32 sectors and1 sector, respectively, so the calculation of steps S3 and S4 is notperformed. At step S5, the file operation system calculates the datalength of the FAT using equations 11 and 12. Here, since the FAT isFAT12, the following calculation is performed.Size    1 = (((((TS − (RSC + RDE))/SC) + 2) × 12/8) + 511)/512   = (((((65568 − (1 + 32))/SC) + 2) × 12/8) + 511)/512   = 7  sectors.  

Once the Size 1 has been calculated, at step S6, the file systemoperation unit 9 calculates the NOM using equation 12 so that the masterboot record and the partition boot sector are in different clusters.NOM = (SC − (RSC + RDE + Size  1 × 2)  %  SC) + SC   = (32 − (1 + 32 + 7 × 2)  %  32) + 32   = 49    sectors.

Once the NOM has been calculated, at step S7, the file system operationunit 9 calculates the number of clusters in the regular area using theequation 13.CN = (TS − (RSC + RDE + Size  1 × 2 + NOM))/SC   = (65568 − (1 + 32 + 7 × 2 + 49))/32   = 2046  clusters.  

At step S8, the file system operation unit 9 calculates the data lengthof the FAT using equation 14.  For  FAT12 : Size  2 = (((CN + 2) × 12/8) + 511)/512   = (((2046 + 2) × 12/8) + 511)/512   = 6  sectors.  

At step S9, the file system operation unit 9 compares the Size 1calculated at step S5, and the Size 2 calculate at step S8. Here, Size 1is 7 sectors, and Size 2 is 6 sectors. Since these are not identicalvalues, the file system operation unit 9 moves to step S10, substitutesSize 1 for Size 2, moves to step S6 again and recalculates the NOM.NOM = (SC − (RSC + RDE + Size  1 × 2)  %  SC) + SC   = (32 − (1 + 32 + 6 × 2)  %  32) + 32   = 51  sectors.

Once the NOM has been calculated, at step S7, the file system operationunit 9 calculates the number of clusters in the regular area.CN = (TS − (RSC + RDE + Size    1 × 2 + NOM))/SC   = (65568 − (1 + 32 + 6 × 2 + 49))/32   = 2046    clusters.

At step S8, the data length of the FAT is calculated.For  FAT12 : Size  2 = (((CN + 2) × 12/8) + 511)/512   = (((2046 + 2) × 12/8) + 511)/512   = 6

Following this calculation, at step S9, the file system operation unit 9compares Size 1 and Size 2, and since the two values are identical, theprocessing of the flowchart ends.

As shown above, the present embodiment enables the NOM to be calculatedso that the size of the partition area and the size of the system areaare an integral multiple of the number of erasable blocks, thus ensuringthat clusters are not stored straddling two erasable blocks. Clusterboundaries can be aligned with erasable block boundaries, and theboundary of the volume management information with an erasable blockboundary, so that when one cluster is rewritten or overwritten, thenumber of erasable blocks that needs to be erased is limited to one,thereby reducing the number of times that any one erasable block needsto be erased. Consequently, the time required to write data into thesemiconductor memory card 100 is shortened, and a nonvolatile memory 1with a longer lifespan can be realized.

Second Embodiment

A second embodiment proposes an arrangement in which the volume area isdivided into an area to which the general user can gain access (the userdata area), and an area that stores data securely (the protected area).

A structure of an access apparatus 200 and a semiconductor memory card100 in the second embodiment are shown in FIG. 14. In the internalstructure shown in the drawing, in contrast to that shown in FIG. 3A,the nonvolatile memory 1 has been provided with a protected area, andthe semiconductor memory card 100 and the access apparatus 200 have beenprovided respectively with secure processing units 11 and 12.

The following is an explanation of the secure processing unit 11provided in order to perform secure reading and writing to and from theprotected area in the nonvolatile memory 1. As shown in FIG. 15, thesecure processing unit 11 includes a system area 13, a hidden area 14,an AKE processing unit 15, a Ks decrypting unit 16, and a Ks encryptingunit 17.

The system area 13 is a read-only area storing a media key block (MKB)and a media-ID. The MKB and media-ID stored in this area cannot berewritten. Suppose that the semiconductor memory card 100 is connectedto an access apparatus 200, and the MKB and media-ID is read by thataccess apparatus 200. If the access apparatus 200 correctly performs aspecified calculation using the MKB, the media-ID and a device key Kdheld internally, it can obtain a correct encryption key Kmu.

The hidden area 14 stores a correct value for the encryption key Kmu, inother words the encryption key Kmu that should be obtained if the accessapparatus 200 performs correct calculation using a valid device key Kd.

The AKE (authentication and key exchange) processing unit 15 performsmutual authentication between the access apparatus 200 and thesemiconductor memory card 100 using the challenge-response method,verifies the authenticity of the opposing device, and if the opposingdevice is invalid, stops processing. If the opposing device is valid,however, an encryption key (session key Ks) is shared by the accessapparatus 200 and the semiconductor memory card 100. Authenticationperformed by the access apparatus 200 has three phases. First, in afirst challenge phase, the access apparatus 200 generates a randomnumber, encrypts the random number using the encryption key Kmu, andtransmits the encrypted random number to the semiconductor memory card100 as a challenge value A. Then, in a first response phase, thesemiconductor memory card 100 uses the encryption key Kmu storedinternally to decrypt the challenge value A, and transmits the decryptedvalue to the access apparatus 200 as a response value B. Following this,in a first verify phase, the access apparatus 200 decrypts the challengevalue A held internally using its encryption key Kmu, and compares thedecrypted value with the response value B transmitted from thesemiconductor memory card 100.

Authentication performed by the semiconductor memory card 100 also hasthree phases. First, in a second challenge phase, the semiconductormemory card 100 generates a random number, encrypts the random numberusing the encryption key Kmu, and transmits the encrypted random numberto the access apparatus 200 as a challenge value C. Then, in a secondresponse phase, the access apparatus 200 uses the encryption key Kmustored internally to decrypt the challenge value C, and transmits thedecrypted value to the semiconductor memory card 100 as a response valueD. Following this, in a second verify phase, the semiconductor memorycard 100 decrypts the challenge value C held internally using itsencryption key Kmu, and compares the decrypted value with the responsevalue D transmitted from the access apparatus 200.

If the access apparatus 200 uses an invalid encryption key Kmu toperform mutual authentication, challenge value A and response value B inthe first verify phase and challenge value C and response value D in thesecond verify phase will be judged to be non-matching values, and mutualauthentication will be stopped. If the authenticity of the opposingdevices is verified, however, the AKE processing unit 15 calculates anexclusive OR of challenge value A and challenge value C and obtains thesession key Ks by decrypting the exclusive OR using the encryption keyKmu.

When encrypted data to be written into the protected area is output fromthe access apparatus 200 connected to the semiconductor memory card 100,the Ks decrypting unit 16 uses the session key Ks to decrypt this datawhich has already been encrypted by session key Ks before being output.The data obtained by this decryption is written into the protected area,as the original data.

The Ks encrypting unit 17 receives a command from the access apparatus200 connected to the semiconductor memory card 100 instructing it toread data, encrypts the data stored in the protected area using thesession key Ks, and then outputs the encrypted data to the accessapparatus 200. Reading and writing of data to and from the protectedarea is performed following decryption performed by the Ks decryptingunit 16 and encryption performed by the Ks encrypting unit 17, so theprotected area can only be accessed when the semiconductor memory card100 and a connected access apparatus 200 have performed AKE processingsuccessfully.

Next, the format of the volume area in the second embodiment isexplained, with reference to the detailed drawing of the volume areaincluding the protected area shown in FIG. 16. In the drawing, if thetotal size of the volume area is ‘volume size’, the user data area is anarea ‘volume size×(1−β)’ extending from the start of the volume area,and an area ‘volume size×β’ following the user data area is allocated tothe protected area. Here, β is a value for which the minimum setting is0.01. To take one example, if the volume size is 64 MB and β is 0.01,the protected area is set at 640 KB. The format of the user data areaand the protected area is realized when the file system operation unit 9executes the initialization procedure shown in FIG. 9.

The following describes an example calculation that is performed tocalculate the size of the partition control area and the system area inthe user data area, when the total number of sectors TS in the user dataarea is 124160.

Since the TS is 124160, at step S1, the file system operation unit 9determines the cluster size to be 32 sectors. Once the cluster size hasbeen determined to be 32 sectors, at step S2, the file system operationunit 9 determines that a FAT12 file system should be used by referringto the cluster size SC and the total sector size TS. In theseembodiments the sizes of the RDE and the RSC are fixed respectively at32 sectors and 1 sector, so the calculation of steps S3 and S4 is notperformed. At step S5, the file operation system calculates the datalength of the FAT using equations 11 and 12. Here, since the FAT isFAT12, the following calculation is performed.Size    1 = (((((TS − (RSC + RDE))/SC) + 2) × 12/8) + 511)/512   = (((((124160 − (1 + 32))/32) + 2) × 12/8) + 511)/512   = 12  sectors.  

Once the Size 1 has been calculated, at step S6, the file systemoperation unit 9 calculates the NOM using equation 12 so that the masterboot record and the partition boot sector are in different clusters.$\begin{matrix}{{NOM} = {\left( {{SC} - {\left( {{RSC} + {RDE} + {{Size}\quad 1 \times 2}} \right)\%{SC}}} \right) + {SC}}} \\{= {\left( {32 - {\left( {1 + 32 + {12 \times 2}} \right){\% 32}}} \right) + 32}} \\{= {39\quad{{sectors}.}}}\end{matrix}$

Once the NOM has been calculated, at step S7, the file system operationunit 9 calculates the number of clusters in the regular area using theequation 13. $\begin{matrix}{{CN} = {\left( {{TS} - \left( {{RSC} + {RDE} + {{Size}\quad 1 \times 2} + {NOM}} \right)} \right)/{SC}}} \\{= {\left( {124160 - \left( {1 + 32 + {12 \times 2} + 49} \right)} \right)/32}} \\{= {3877\quad{{clusters}.}}}\end{matrix}$

At step S8, the file system operation unit 9 recalculates the datalength of the FAT using equation 14. For  FAT12: $\begin{matrix}{{{Size}\quad 2} = {\left( {\left( {\left( {{CN} + 2} \right) \times {12/8}} \right) + 511} \right)/512}} \\{= \left( {\left( {\left( {3877 + {2 \times {12/8}}} \right) + 511} \right)/512} \right.} \\{= {12\quad{{sectors}.}}}\end{matrix}$

At Step S9, the file system operation unit 9 compares the Size 1calculated at step S5, and the Size 2 calculated at step S8. Here, bothSize 1 and Size 2 are calculated to be 12 sectors, so they are judged tobe identical values and the processing of the flowchart ends.

A layout of the protected area when the system area, and the partitioncontrol area are formed with a TS, Size 1, and NOM sized as calculatedby the aforementioned calculations, is shown in FIG. 17. If this drawingis compared with FIG. 12, it can be seen that the size of the duplexedFAT has increased from 14 to 24 sectors, while the size of the reservedinformation 1/2 and 2/2 has shrunk from 17 to 7 sectors, so that thepartition control area and the system area fit exactly into threeerasable blocks.

The following describes an example calculation that is performed tocalculate the size of the partition control area and the system area inthe protected area, when the total number of sectors TS in the user dataarea is 1280.

Since the TS is determined to be 1280, at step S1, the file systemoperation unit 9 determines the cluster size to be 2 sectors (1 KB ofmemory, and only {fraction (1/16)}th the size of the user data area).Once the cluster size has been determined to be 2 sectors, at step S2,the file system operation unit 9 determines that a FAT12 file systemshould be used by referring to the cluster size SC and the total sectorsize TS. In these embodiments, the sizes of the RDE and the RSC arefixed at 32 sectors and 1 sector, respectively, so the calculation ofsteps S3 and S4 is not performed. At step S5, the file operation systemcalculates the data length of the FAT using equations 11 and 12. Here,since the FAT is FAT12, the following calculation is performed.$\begin{matrix}{{{Size}\quad 1} = {\left( {\left( {\left( {\left( {\left( {{TS} - \left( {{RSC} + {RDE}} \right)} \right)/{SC}} \right) + 2} \right) \times {12/8}} \right) + 511} \right)/512}} \\{= {\left( {\left( {\left( {\left( {\left( {1280 - \left( {1 + 32} \right)} \right)/2} \right) + 2} \right) \times {12/8}} \right) + 511} \right)/512}} \\{= {2\quad{{sectors}.}}}\end{matrix}$

Once the Size 1 has been calculated, at step S6, the file systemoperation unit 9 calculates the NOM using equation 12 so that the masterboot record and the partition boot sector are in different clusters.$\begin{matrix}{{NOM} = {\left( {{SC} - {\left( {{RSC} + {RDE} + {{Size}\quad 1 \times 2}} \right)\%{SC}}} \right) + {SC}}} \\{= {\left( {2 - {\left( {1 + 32 + {2 \times 2}} \right){\% 2}}} \right) + 2}} \\{= {3\quad{{sectors}.}}}\end{matrix}$

Once the NOM has been calculated, at step S7, the file system operationunit 9 calculates the number of clusters in the regular area using theequation 13. $\begin{matrix}{{CN} = {\left( {{TS} - \left( {{RSC} + {RDE} + {{Size}\quad 1 \times 2} + {NOM}} \right)} \right)/{SC}}} \\{= {\left( {1280 - \left( {1 + 32 + {2 \times 2} + 3} \right)} \right)/32}} \\{= {620\quad{{clusters}.}}}\end{matrix}$

At step S8, the file system operation unit 9 calculates the data lengthof the FAT using equation 14. For  FAT12: $\begin{matrix}{{{Size}\quad 2} = {\left( {\left( {\left( {{CN} + 2} \right) \times {12/8}} \right) + 511} \right)/512}} \\{= {\left( {\left( {\left( {620 + 2} \right) \times {12/8}} \right) + 511} \right)/512}} \\{= 2}\end{matrix}$

At Step S9, the file system operation unit 9 compares the Size 1calculated at step S5, and the Size 2 calculated at step S8. Here, Size1 and Size 2 are both calculated to be 2 sectors, so they are judged tobe identical values and the processing of the flowchart is completed.

A layout of the protected area when the system area, and the partitioncontrol management area are formed with a TS, Size 1, and NOM sized ascalculated by the aforementioned calculations, is shown in FIG. 18. Inthis embodiments, both the user data area and the protected area have apartition control area, a system area, and a protected area, so each istreated as an independent physical medium by the access apparatus 200.Thus, although the user data area and the protected area have differentcluster sizes, the boundaries of clusters in both the user data area andthe protected area can be aligned with the boundaries of erasableblocks.

In the above embodiment, even if the volume area includes two areas, theuser data area and the protected area, the boundaries of such areas arealigned with the boundaries of erasable blocks, and so rewriting ofclusters can be completed in a short time. In addition, the number oftimes that erasable blocks need to be erased is reduced, so that thelifespan of the nonvolatile memory is not needlessly shortened.

Third Embodiment

The third embodiment relates to an improvement used when data stored inerasable blocks is erased, the erasable blocks being managed using alogical address and a physical address. A structure of an access controlunit 2 in the third embodiment is shown in FIG. 19. The access controlunit 2 in the drawing includes a command decoding unit 21, alogical/physical address conversion unit 22, a read control unit 23, anallocation changing unit 24, a write control unit 25, an erase controlunit 26, and a modify control unit 27.

The command decoding unit 21 receives a command issued by an accessapparatus 200, and decodes the original content of the command at thepoint of issue. If a read command is received, the command decoding unit21 instructs the read control unit 23 to read data from the nonvolatilememory 1 (Read). If a write command is received, the command decodingunit 21 instructs the write control unit 25 to write data into thenonvolatile memory 1 (Write). If a write command specifying an unerasedblock as an access target is received, the command decoding unit 21instructs the modify control unit to modify (rewrite) data stored in thenonvolatile memory 1 (Modify). If an obtain status command is received,the command decoding unit 21 instructs the allocation changing unit 24to read an erased block list (described later in this specification). Ifan erase command is received, the command decoding unit 21 instructs theallocation changing unit 24 to erase the specified erasable block.

The logical/physical address exchanging unit 22 has an addresscorrespondence table showing correspondences between logical andphysical addresses for erasable blocks. When a logical address that isto be accessed is specified by the access apparatus 200, thelogical/physical address exchanging unit 22 refers to the correspondencefor the logical address shown in the address correspondence table,exchanges the logical address for a corresponding physical address, andoutputs the physical address to the read control unit 23, the allocationchanging unit 24, and the modify control unit 27.

When a read command is issued by the access apparatus 200, the writecontrol unit 23 performs control so as to have the access apparatus 200read data stored in the read location specified by the read command.

The allocation changing unit 24 holds an erased block list in whichphysical addresses for erasable blocks that have been erased arearranged in a first in, first out (FIFO) format. When a read command isissued by the access apparatus 200, the allocation changing unit 24judges whether a physical address corresponding to the logical addressspecified as a read destination is present in the erased block list. Ifsuch a physical address is judged to be present, the allocation changingunit 14 outputs the physical address to the write control unit 25, anddeletes the physical address from the erased block list. If thecorresponding physical address indicates an erasable block that has notyet been erased, the allocation changing unit 24 allocates a physicaladdress at the start of the erased block list to the logical address asthe read destination, and outputs the allocated physical address to theread control unit 25, while adding the physical address that waspreviously allocated to the logical address as the read destination tothe end of the erased block list. Furthermore, when a obtain statuscommand is issued by the access apparatus 200, the allocation changingunit 24 changes physical addresses shown in the erased block list tological addresses, and outputs an erased block list, indicating erasederasable blocks by using a table of logical addresses, to the accessapparatus 200. If an erase command indicating a logical address hasalready been issued by the access apparatus 200, the allocation changingunit 24 controls operations so that a physical address corresponding tothis logical address is added to the erased block list.

The write control unit 25 writes data into the nonvolatile memory 1 inaccordance with the physical address output from the allocation changingunit 24, when a write command to write a block is received.

The erase control unit 26 performs polling at fixed intervals todetermine whether a physical address for an unerased block has beenadded to the erased block list. If such a physical address has beenadded, the erase control unit 24 erases the erasable block indicated bythe physical address.

The modify control unit 27 reads data from the nonvolatile memory 1 tothe work memory 3, and modifies the data while it is being held in thework memory 3, before writing the modified data from the work memory 3to the nonvolatile memory 1, when a write command to modify an erasableblock in which data is already written is received. The modifyprocessing performed by the modify control unit 27 is realized bycooperative processing with the allocation changing unit 24. The flow ofthe data modify processing performed by the modify control unit 27 isshown in time sequence in FIG. 20.

In the initial state shown in FIG. 20A, data is currently stored inshaded blocks (blocks with physical addresses 001, 002, 004, 007 to015), and the remaining blocks 003, 005, and 006 have been erased.Physical addresses 003, 005, and 006 representing erased blocks arearranged in the erased block list. In an address correspondence tableshowing correspondences between logical and physical addresses, thelogical addresses 001, 002, 003, 004, and 005 correspond respectively tophysical addresses 001, 002, 003, 004, and 005.

Here, if a write command indicating that a different value is to bewritten into an erasable block with the logical address 001 is issued bythe access apparatus 200, the write control unit 25 transfers the datawritten in the block with the logical address 001 from the nonvolatilememory 1 to the work memory 3 (see arrow (1) Read in FIG. 20A). Then,the write control unit 25 modifies the data written in the block withthe logical address 001 while this block is held in the work memory 3(see arrow (2) Modify in FIG. 20A).

Next, in FIG. 20B, the modify control unit 27 reads a physical address003 at the front of the erased block list, as shown by an arrow BN1, andwrites data into the block indicated by the physical address 003, asshown by arrow (3) Write. Then, in FIG. 20C, the modify control unit 27arranges the physical address 001, whose corresponding block should beerased, in the erased block list, as shown by arrow (4).

Lastly, the modify control unit 27 interchanges logical address/physicaladdress correspondences, as shown in FIG. 20D. Here, the physicaladdress 003 is allocated to logical address 001, and the physicaladdress 001 is allocated to logical address 003. Data can thus beoverwritten into the logical address 001 by writing data into thephysical address 003, and then switching the correspondences betweenlogical and physical addresses.

The following is an explanation of the internal structure of the accessapparatus 200. FIG. 21 shows an internal structure of a file systemoperation unit 9 in the access apparatus 200 of the third embodiment.The file system operation unit 9 shown in the drawing includes a filedeleting unit 28, and a precedent erase control unit 29.

The file deleting unit 28 deletes files by updating a FAT read from theprimary memory 7, and writing the updated FAT into the semiconductormemory card 100. If the application program 8 issues an instruction todelete a file, the file deleting unit 28 executes file deletion bysetting FAT entries corresponding to clusters storing sections of thisfile at ‘0’, indicating that these clusters are unused. However, theclusters (erasable blocks) storing file sections have not been returnedto a blank state, so the clusters must first be erased before anotherfile can be recorded in the same clusters. Therefore, the amount of timerequired for erasure processing increases proportionally with increasesin the number of times that an old file is deleted and a new file isrecorded.

The precedent erase control unit 29 issues an obtain status command tothe semiconductor memory card 100, instructing it to read the erasedmemory free list, while waiting for an instruction from the applicationprogram 8. Once the command has been issued, and the erased memory freelist output, the precedent control unit 29 receives the output erasedfree list, and compares it with the FAT to specify erasable blockscorresponding to clusters that are set as unused in the FAT. (When oneerasable block includes a plurality of clusters, only erasable blocksformed entirely from unused clusters can be specified). Then, of theseerasable blocks, blocks that are not present in the erased block listare also specified. The blocks are erasable blocks that are both unusedand unerased, and the precedent erase control unit 29 issues an erasecommand to the semiconductor memory card 100 instructing that suchblocks be erased. The erase command includes a logical addressspecification, and an instruction to add a physical addresscorresponding to this logical address to the erased block list. If aphysical address is added to the erased block list by issuing such anerase command, the block indicated by the erase command is erased in thesame way as other unused and unerased erasable blocks, when polling isperformed by the erase control unit 26. The same procedure is performedfor all unused and unerased blocks. The detailed procedure performed bythe precedent erase control unit 29 is explained below, with referenceto the flowchart of FIG. 22.

In this embodiment, if the precedent erase control unit 29 is activated,it moves to the loop processing of steps S21 to S22. At step S21, theprecedent erase control unit 29 judges whether an access instruction hasbeen received from the application program 8, and at step S22, judgeswhether a predetermined polling time has passed. If an instruction hasbeen received from the application program 8, the precedent erasecontrol unit 29 moves to step S23, and performs a file system operationand access of the semiconductor memory card 100 in accordance with theinstruction. If the predetermined polling time has passed, the precedenterase control unit 29 moves from step S22 to step S24, and issues anobtain status command for reading the erased free list to thesemiconductor memory card 100. Following this, at step S25, theprecedent erase control unit 29 is in a wait state, waiting for theerased block list to be read. Once the erased block list has been read,at step S26 the precedent erase control unit 29 specifies logicaladdresses for all erasable blocks that are formed from clusters set asunused in the FAT and that are not present in the erased block list.

At step S27, the precedent erase control unit 29 judges whether unusederasable blocks that have not yet been erased exist, and if no suchblock exists, returns immediately to the loop processing of steps S21 toS22. If such blocks exist, the precedent erase control unit 29 performsthe loop processing of steps S28 to S30. In other words, the precedenterase control unit 29 issues erase commands to the semiconductor memorycard 100 stipulating erasure of data at each of the physical addressesfor the unused and as yet unerased erasable blocks specified at stepS26. Once these commands have been issued, the physical addresses foreach of these blocks are added to the erased block list, and are subjectto erasure.

The following is amore detailed explanation of the above operation ofthe precedent erase control unit 29, described with reference to FIGS.23A and 23B. In an initial state shown in FIG. 23A, an address 0001 foran erasable block is set in the FAT as being in use, and physicaladdresses 0003, 0005, and 0006 are arranged in the erased block list asaddresses of erased blocks. Data is stored in blocks in the file systemthat are shaded in the drawing (addresses 0000, 0001, 0002, 0004). Inthis state, if there is no instruction from the application program 8,and the predetermined polling time has passed (step S21, No, step S22,Yes), the file system operation unit 9 in the access apparatus 200 readsthe erased block list by issuing an obtain status command to thesemiconductor memory card 100 (step S24), and compares the read erasedblock list with the FAT (step S25). As a result of this comparison,blocks that are set as unused in the FAT and whose logical addresses donot exist in the erased block list (erasable blocks with addresses 0000,0002, 0004) are specified (step S26). Since these blocks are not in use,the file system operation unit 9 issues erase commands to thesemiconductor memory card 100 to have these erasable blocks erased(steps S28 to S30). Consequently, the addresses 0000, 0002, and 0004 areadded to the erased block list, as shown in FIG. 23B, and the erasableblocks indicated by these addresses are erased.

In the above embodiment, the access apparatus 200 reads the erased blocklist from the semiconductor memory card 100, and compares the FAT withthe read erased block list in order to specify unused erasable blocksthat have not yet been erased, and instructs the semiconductor memorycard 100 to erase these blocks. As a result, the file system operationunit 9 can erase unused erasable blocks that are still unerased whilewaiting for an instruction from the application program 9, and soerasure of the unused blocks can be performed more efficiently.

In addition, erasure of unused blocks can be performed whenever theaccess apparatus 200 is free, so that the opportunities for performingblock erasure can be greatly increased. As a result, there is no dangerof there being insufficient physical addresses in the erased block list,and the efficiency of processing performed when blocks are modified andoverwritten is greatly improved.

In the access apparatus 200 of this embodiment, the erased block list isread from the semiconductor memory card 100, and unused and as yetunerased blocks are specified. However, the erase control unit 26 insidethe access control unit 2 of the semiconductor memory card 100 mayspecify blocks that are both unused and unerased by referring to theFAT, and then delete such blocks. Here, the access control unit 2exchanges physical addresses included in the erased block list forlogical addresses, and passes the exchanged addresses to the accessapparatus 200. However, the erased block list and the addresscorrespondence table may be passed to the access apparatus 200, andexchange of physical addresses for logical addresses performed in theaccess apparatus 200. Data erasure may be performed when a file isdeleted, or as parallel processing when another command is beingexecuted. Furthermore, other information such as an unerased block listthat manages the physical addresses of unerased erasable blocks may beused instead of the erased block list that manages the physicaladdresses of erased erasable blocks. This embodiment is described usinga FAT, but information may be stored as a list or other similar format.

Fourth Embodiment

The fourth embodiment describes an improvement realized when theprocessing of the third embodiment is performed using an erased blocktable instead of an erased block list. FIG. 24 shows an internalstructure for an access apparatus 200 2 in the fourth embodiment. Ifthis drawing is compared with FIG. 19, it can be seen that the erasedblock list has been replaced by an erased block table. The erased blocktable in the fourth embodiment is formed from entries corresponding toeach erasable block. If a block is erased, the corresponding entry isset at ‘1’ and if a block is unerased, the corresponding entry is set at‘0’. The erased block table expresses the erase state of each erasableblock by setting either ‘1’ or ‘0’ in the erased block table.

As a result of the erased block list having been replaced by the erasedblock table, the processing performed by the write control unit 25 andthe erase control unit 26 in the fourth embodiment differs from thatperformed in the third embodiment in the following respect.

When a write command is generated by the access apparatus 200, the writecontrol unit 25 in the fourth embodiment refers to the erased blocktable and judges whether the write destination specified by the commandis erased, and whether it is an unused block. Then, if the writedestination block is an unerased block, the write control unit 25 hasthe erase control block 26 erase data from the block before writing newdata into the block. In other words, the write control unit 25 of thefourth embodiment erases data before performing a data write.

Next, the processing of the precedent erase control unit 29 in thefourth embodiment is explained. The precedent erase control unit 29performs erasure of erasable blocks while waiting for instructions fromthe application program 8. The erasing procedure is the same as thatdescribed in the third embodiment, and is shown in the flowchart of FIG.25. This flowchart is identical to that shown in FIG. 22, apart from thefact that ‘erased block list’ has been changed to ‘erased block table’,and since there is no great variation in content, a detailed descriptionis omitted here. Next, the processing performed by the precedent erasecontrol unit 29 in the fourth embodiment is described with reference toFIGS. 26A and 26B.

In an initial state shown in FIG. 26A, a block with an address 0001 ismanaged as a block in use, and blocks with addresses 0003, 0005, and0006 are managed in the erased block table as blocks from which data hasbeen erased. Data is stored in blocks in the nonvolatile memory thathave been shaded in the drawing (addresses 0000, 0001, 0002, 0004). Inthis initial state, if blocks which are not in use but contain dataexist, and write commands to write data into these unused blocks aregenerated, data erasure processing is required. In this embodiment, ifthe precedent erase control unit 29 is waiting for an instruction fromthe application program 8, and the predetermined polling time has passed(step S21, No, step S22, Yes), the precedent erase control unit 29 readsthe erased block table by issuing an obtain status command to thesemiconductor memory card 100 (step S24), and compares the read erasedblock table with the FAT (step S25). As a result of this comparison,blocks that are set as unused in the FAT and whose logical addresses arenot managed by the erased block table (erasable blocks with addresses0000, 0002, 0004) are found (step S26). In FIG. 26, ‘0’ is set in boththe FAT and the erased block table for blocks with addresses 0000, 0002,and 0004, so these blocks are unused and as yet unerased blocks. Sincethese blocks are not in use, and thus contain data that may be safelyerased, the precedent erase control unit 29 issues erase commands, toset a value ‘1’ for each of the corresponding addresses in the erasedblock table, indicating that these blocks are to be erased (steps S28 toS30). As a result, all the data in unused blocks is erased, and theseblocks are then managed by the erased block table as erased blocks.Therefore, procedure for performing data writing by allocating unusedblocks described later in this specification can be performed withoutrequiring any erasure processing, and high-speed data writes can beachieved.

Fifth Embodiment

The fifth embodiment proposes a solution to the problem of filefragmentation. File fragmentation conventionally refers to the processin which a file is divided into a plurality of file sections and thesesections are then stored non-consecutively in the memory. If a pluralityof file sections are stored non-consecutively on a recording medium suchas an optical disc or a magnetic disc, a large number of disc seeks arerequired to read the non-consecutively stored file sections, and theread processing time is lengthened. In order to resolve the problemscreated by such fragmentation, the file system operation unit 9 readsthe non-consecutively stored file sections, and stores them againconsecutively in the memory (defragmentation). If the above processingis performed, the file sections forming a file can be read smoothlywithout requiring any disc seeks to be performed, enabling data to beread at high speed. This completes the summary of the solution providedto resolve the problem of fragmentation in discs. Next, fragmentationoccurring in the semiconductor memory card 100 is considered. Discseeking is not required when reading data from the semiconductor memorycard 100, so if the file sections are stored non-consecutively, there isno likelihood that processing will be lengthened for this reason.

However, although disk seeks are not a problem, fragmentation causesboth 1. overhead generated when commands are issued, and 2. cache missesgenerated when the FAT is read (both described in more detail below) toincrease considerably, thereby lengthening the time required to read afile.

1. Overhead Generated when Commands are Issued

The impact that fragmentation has on the overheads generated whencommands are issued can be more easily understood if described withreference to FIGS. 27A and 27B. FIG. 27A illustrates a situation inwhich a 48 KB file is divided into three 16 KB file sections and storedat random in three areas. FIG. 27B illustrates a situation in which a 48KB file is stored in consecutive memory areas. In FIGS. 27A and 27B, thefile system operation unit 9 issues a read command in the format ‘Read(add, size)’ to the nonvolatile memory to have a data read performed.Here, ‘add’ represents a logical address of a read destination, and‘size’ represents the size of the data that is to be read. The timetaken by each read command is the sum of a data read time that isproportional to the length of the read data, and a fixed overhead timerequired to issue the read command. In the data arrangement shown inFIG. 27A, a file 1 must be read by issuing three read commands:‘Read(0000, 16 KByte)’, ‘Read(0002, 16 KByte)’, and ‘Read(0004, 16KByte)’. This means that the time required to read this file is 36 ms(=(8+4)×3). On the other hand, if data is arranged as in FIG. 27B, theentire 48 KB of data for the file can be read simply by issuing onecommand ‘Read(0000, 48 KByte)’. Consequently, the time taken to read thefile in this case is 28 ms (=(8×3+4)). Thus, it can be seen that theoverhead generated when commands are issued increases in proportion todegree of randomness with which file sections are stored.

2. FAT Cache

A FAT cache is an anticipatory read of the FAT arranged in the systemarea of the semiconductor memory card 100 to the internal memory of theaccess apparatus 200, which allows the FAT to be referred to at highspeed by accessing the internal memory. The FAT is cached frequently ifthe access apparatus 200 is a portable device with a small-scaleinternal memory. The FAT is cached by sequentially reading sections ofthe FAT that have been stored consecutively in the memory. However, ifFAT fragmentation has been generated, caching the FAT will involvereading both sections containing the FAT and sections contained otherdata in order to the internal memory. If data other than FAT sections isread to the internal memory, a large quantity of data which is not theobject of the cache will be read, thereby generating a cache miss. If alarge number of such cache misses are generated, the number of reads tothe internal memory will increase correspondingly, and so the timerequired to read the FAT will be lengthened.

Despite the present of these two problems, applying the same means toresolve fragmentation in the semiconductor memory card 100 as was usedto solve the problem in a disc is not a wise course of action. Thereason for this is that modifying data stored in blocks in thesemiconductor memory card 100 requires erasure of the stored data, andsuch erasure requires a longer processing time than is required whenequivalent processing is performed on a disc. In this embodiment,changing the correspondences between physical addresses and logicaladdresses is proposed as a countermeasure to combat the increases incommand overheads and cache misses generated when fragmentation occurs.In other words, the correspondences between physical addresses andlogical addresses are changed so that the blocks in which FAT sectionsare stored can be shown consecutively using logical addresses, withoutneeding to change their physical arrangement in the memory.

When a 48 KB file is divided into three 16 KB sections and stored inthree separate memory areas, as in FIG. 27A, the access apparatus 200can read the file sections stored in these three areas (blocks) providedthat the logical addresses for the blocks are indicated consecutively.Reading is performed by issuing one read command indicating the first ofthe plurality of logical addresses, and the data length of the file(here 48 KB). Furthermore, if the FAT is divided into three sections,and stored in three memory areas (blocks), the access apparatus 200 canread non-consecutively stored FAT sections to the internal memory inorder, provided that the logical addresses for the blocks are indicatedconsecutively. Here, reading is performed by issuing read commandsindicating each of the consecutive logical addresses as readdestinations in turn. If such processing is performed, cache misses areno longer generated. Thus, even if a plurality of file and FAT sectionsare stored at random in a plurality of areas, these areas can beallocated consecutive logical addresses, resolving the problem ofoverheads generated when read commands are issued, and enabling thegeneration of cache misses to be avoided.

The processing performed by the precedent erase control unit 29 toresolve the issue of fragmentation using logical addresses is explainedwith reference to the procedure shown in the flowchart of FIG. 28. FIG.29, which shows actual objects to which variables t, u, v, and y in theflowchart correspond, is also referred to during this explanation. Atstep S50, the precedent erase control unit 29 sets initial values forthe variables x and y (x←1, y←1) This means that processing is to beperformed on a first section of a first file. Next, at step S51, theprecedent control unit 29 compares positions of a logical address s,corresponding to a block storing a yth section of an xth file, and alogical address t, corresponding to a block storing a y+1th section ofthe xth file, to determine whether these blocks are adjacent. When, asshown in FIG. 29A, the yth section and the y+1th section are stored innon-adjacent erasable blocks, in the order of y→y+1, step S52 is Yes,and the precedent erase control unit 29 moves to step S54.

When the sections are stored in the order y+1→y, as shown in FIG. 29B,the precedent erase control unit 29 moves to step S53, and allocates aphysical address u to the logical address t, and a physical address v tothe logical address s. As a result, the allocation of physical addressesto logical addresses changes as shown by the arrows rv1 and rv2 in FIG.29B. Next, at step S54, the precedent erase control unit 29 judgeswhether the logical address of the erasable block storing the ythsection, and the logical address of the erasable block storing the y+1thsection are consecutive. If the erasable block storing the y+1 sectionimmediately follows the erasable block storing the yth section, as shownin FIG. 29C, a relationship s+1=t is established, so that step S54 isYes, and processing moves to step S56. If the erasable blocks storingthe yth section and the y+1th section are non-adjacent, the relationships+1=t is not established, so step S54 is No, and processing moves tostep S55. Here, if a physical address corresponding to the logicaladdress s+1 is w, at step S55, the physical address v for the erasableblock storing the y+1th section is allocated to the logical address s+1,and the physical address w is allocated to the logical address t. If theprocessing of step S55 is executed when the yth and the y+1th sectionsare stored as shown in FIG. 29D, address correspondences are changed asshown by the arrows rv3 and rv4.

Once the above processing has been completed, at step S56, the precedenterase control unit 29 judges whether the variable y is a last sectionnumber. If y is not the last number, the precedent erase control unit 29increments y at step S57, and processing moves to step S51. Theprocessing of steps S51 to S57 is repeated for each of the sections inan xth file by performing the check of step S56, and the incrementing ofy at step S57.

If, on the other hand, step S56 is Yes, the precedent control erase unit29 judges whether x is the last file number, at step S58, and if theanswer is No, moves to step S59, increments the variable x (x←x+1), andsets an initial value for the variable y at step S60. Thus, theprocessing of steps S51 to S57 is repeated for all files by performingthe check of step S58, and the incrementing of the variable y at stepS59.

The resolution to the problems posed by fragmentation proposed in thisembodiment is explained with reference to an actual example shown inFIG. 30. In the initial state shown in FIG. 30A, sections file 1-1/3,file 1-2/3, and file 1-3/3 forming a file 1 are stored in erasableblocks corresponding to logical addresses 0000, 0001, and 0004. Inaddition, sections file 2-1/4, file 2-2/4, file 2-3/4, and file 2-4/4forming a file 2 are stored in erasable blocks corresponding to logicaladdresses 0002, 0003, 0005, and 0006.

Section file 2-1/4 is stored in an erasable block corresponding to anaddress (logical address 0002) following the logical address 0001 inwhich file section file 1-2/3 is stored, and section file 1-3/3 isstored in an erasable block corresponding to a logical address 0004.

If the processing in the flowchart of FIG. 28 is applied to the examplein this drawing, sections file 1-1/3 and file 1-2/3 correspondrespectively to the logical addresses 0000, and 0001, so that thesesections are arranged in the same order as the corresponding logicaladdresses, and their correspondences are not interchanged. However, ifthe relationship between sections file 1-2/3, and file 1-3/3 isconsidered, it can be seen that while the erasable block storing thesection file 1-2/3 corresponds to the logical address 0001, the erasableblock corresponding to the next logical address 0002 is file 2-1/4.Consequently, step S54 is No, and processing moves to step S55. Then, atstep S55, the correspondence between the logical and physical addressesof the erasable block storing the section file 1-3/3, and thecorrespondence between the logical and physical addresses of theerasable block storing the section file 2-1/4 are interchanged. As aresult, the sections file 1-2/3, and file 1-3/3 can be shown byconsecutive logical addresses, so that the physical address 0002 of theerasable block storing the file section file 2-1/4 is allocated thelogical address 0004, and conversely the physical address 0004 of theerasable block storing the section file 1-3/3 is allocated the logicaladdress 0002. The correspondences between physical and logical addressesfollowing this change are shown in FIG. 30B. Once processing for sectionfile 1-3/3 has been completed, the processing for section file 2-2/4 isperformed. In FIG. 30B, the relationship between sections file 2-1/4,and file 2-2/4 is such that section file 2-1/4 is stored in an erasableblock corresponding to the logical address 0004, and the next sectionfile 2-2/4 is stored in an erasable block corresponding to the logicaladdress 0003. Thus, the logical addresses attached to these sectionsshould be in the reverse order. As a result, step S52 is No, andprocessing moves to step S53, where the order of addresses correspondingto the sections file 2-1/4, and file 2-2/4 is interchanged. Here, thephysical address 0002 corresponding to an erasable block storing thesection file 2-1/4 is allocated to the logical address 0003, and thephysical address 0003 corresponding to the erasable block storing thesection file 2-2/4 is allocated to the logical address 0004. As a resultof this processing, the file sections forming files 1 and 2 are allindicated by consecutive logical addresses.

In this embodiment, even if file sections are stored in non-consecutivememory areas, these memory areas can be allocated consecutive logicaladdresses, thereby reducing the overheads generated when read commandsare issued, and cache misses occurring when the FAT and files arecached.

Sixth Embodiment

The sixth embodiment describes an improvement applied when a variety ofcontents are recorded in the nonvolatile memory via a distributionservice, and the recorded contents reproduced on a portable player. Inthis case, files having a variety of attributes, such as music, images,games, and text, are likely to be stored on the semiconductor memorycard 100. Should there be differences in whether files are readable oreditable depending on file type, the file system operation unit 9 in theaccess apparatus 200 needs to check the contents of the file beforeperforming reading or editing. If such a check is required each time afile is read or edited, the processing performed by the file systemoperation unit 9 will become complicated. Consequently, universal discformat (UDF) used in digital versatile discs (DVDs) sets an extendedattribute for each file, enabling the type of data stored in a file tobe recognizable at a glance, without there being any need to check thecontents of the file.

FIG. 31 shows an example of an extended attribute. The attribute shownin the drawing is a new type of extended attribute formed based on animplementation use extended attribute in the UDF. The extended attributeincludes an attribute type 2000, an attribute subtype 2010, a reservedarea 2020, an attribute length 2030, an implementation use length 2040,an implementation identifier 2050 (these are identical to fields in theimplementation use extended attribute in the UDF, so a more detailedexplanation is omitted here), and an implementation use 2060. Theimplementation use 2060 includes a header checksum 2061 storing achecksum for the header section of the extended attribute, a name 2063storing a file name, and a flag 2062 storing a file attribute. Each bitin the flag 2062 is set at ‘0’ or at ‘1’ to illustrate a file attribute.The first bit of the flag 2062 shows whether the corresponding file is atext file, the second bit shows whether the corresponding file is animage file, and an area from the third bit onward is a reserved area.

If this extended attribute is stored in the semiconductor memory card100, one difficulty is immediately evident. This is that the volumemanagement information of the semiconductor memory card 100 is compliantwith the data structure set out in the ISO/IEC 9293 standard, aspreviously explained, and so there is no provision for giving each filean extended attribute.

In this embodiment, the extended attribute is stored in at least one ofthe protected area and a backup area. The protected area has alreadybeen explained in the second embodiment, so further explanation isomitted here. The backup area is managed separately from the normalpartition in the user area. When a defective sector appears in the userarea of the nonvolatile memory, the allocation changing unit 24, choosesa sector from the backup area to replace the defective sector. FIG. 32shows an internal structure of a semiconductor memory card 100 that isprovided with the defective sector. New extended attributes that cannotbe defined in a FAT file system can be set for each file by storing suchattributes in the protected area or the backup area. Furthermore, sincethe user area and user data area used by a general user utilize aconventional file system that is totally independent of the newly setextended attributes, the system is compatible with other systems. Inaddition, since the access apparatus 200 need only implement theoperations necessary for each file type, fewer operations areimplemented by the access apparatus 200, thereby enabling the memorysize of the access apparatus 200 to be reduced. Furthermore, since thefile type for each file can be judged just by referring to the extendedattribute information rather than referring to the contents of the file,high-speed operations can be realized.

Seventh Embodiment

This embodiment proposes that files in a FAT file system be set as writeprohibited and read prohibited to further improve file protection. In aconventional FAT file system, attributes for individual files, such aswrite prohibited and read prohibited, can be set in file entries. Thefile system operation unit 9 in the access apparatus 200, when connectedto the semiconductor memory card 100, reads and holds volume managementinformation, and refers to the file attribute for a particular file tojudge whether the file can be read or written. Provided that theapplication program 8 in the access apparatus 200 accesses thesemiconductor memory card 100 via the file system operation unit 9, theattributes in the file entries are valid. However, if the applicationprogram 8 accesses the semiconductor memory card 100, bypassing the filesystem operation unit 9 and performing a write or read by issuing adirect write or read command to the semiconductor memory card 100, anywrite prohibited or read prohibited attributes set in the file entrieswill be meaningless. Here, this embodiment proposes that thesemiconductor memory card 100 be structured as shown in FIG. 33, so thatwrite prohibited and read prohibited attributes will be valid even ifthe application program 8 accesses the semiconductor memory card 100directly. FIG. 33 shows an internal structure of a semiconductor memorycard 100 in the seventh embodiment. The characteristics of this drawingare that the nonvolatile memory 1 has a backup area, which contains ablock attribute table.

The block attribute table is made up of entries corresponding toerasable blocks included in the volume area. If an entry is set at ‘1’,the corresponding block is write prohibited. Furthermore, if an entry isset at ‘2’, the corresponding block is read prohibited. The file systemoperation unit 9 and the access control unit 2 disclosed in the fifthembodiment perform operations on the block attribute table, as well ason file entries. If the application program 8 instructs the file systemoperation unit 9 to open a file for which an attribute has been set, thefile system operation unit 9 sets the attribute in the file entrycorresponding to this file. For example, if the application program 8has been instructed to set a file as write prohibited, the attribute forthe corresponding file entry is set as write prohibited. If theapplication program 8 has been instructed to set a file as readprohibited, the attribute for the corresponding file entry is set asread prohibited. If the application program 8 has been instructed to seta hidden attribute, the file system operation unit 9 sets a readprohibited attribute in the corresponding file entry.

If file attributes are set in file entries in this fashion, the filesystem operation unit 9 divides a file into cluster-sized sections, andrecords these sections in a plurality of clusters in the user area.Following recording of the file sections in the clusters, the filesystem operation unit 9 sets the file attribute in entries in the blockattribute table that correspond to each of the erasable blocks in whichthe file is stored. If writing of the file is prohibited, the filesystem operation unit 9 sets a write prohibited attribute in entriescorresponding to each of the clusters storing the file sections, and ifthe file attribute is read prohibited, sets a read prohibited attributein entries corresponding to each of the clusters storing the filesections. If the file attribute is a hidden attribute, the file systemoperation unit 9 sets a read prohibited attribute in entriescorresponding to each of the clusters storing the file sections.

If the file is recorded in the user area in this way, data is read fromor written to blocks according to attributes shown in the blockattribute table. In other words, if a read command is issued by theaccess apparatus 200, the read control unit 23 refers to an entry in theblock attribute table corresponding to the read destination address. Ifthe entry shows that reading is permitted, the read control unit 23reads data from the block shown by the read destination address, or ifthe entry shows that reading is prohibited, does not read data from theblock shown by the read destination address.

If a write command is issued by the access apparatus 200, the writecontrol unit 25, or the modify control unit 27, refers to the entry inthe block attribute table corresponding to the write destinationaddress. If the entry shows that writing is permitted, the write controlunit 25, or the modify control unit 27, writes data into the block shownby the write destination address, and if the entry shows that writing isprohibited, does not write data into the block shown by the writedestination address.

This kind of write and read control can be performed both when theapplication program 8 issues a write or read command via the file systemoperation unit 9, and when the application program 8 issues a write orread command directly, bypassing the file system operation unit 9. Thuswriting and reading of blocks can be restricted whether the accessapparatus 200 issues commands via the file system operation unit 9 ornot. The file system operation 9 in the present embodiment is explainedwith reference to an actual example in FIG. 34. In FIG. 34A, datacontained in a file 1 is stored in erasable blocks with addresses 0000,0002, and 0003, data contained in a file 2 is stored in erasable blockswith addresses 0001 and 0004, data contained in a file 3 is stored in anerasable block with an address 0005, and data contained in a file 4 isstored in an erasable block with an address 0006. FIG. 34B shows asituation, when a file 1, for which a write prohibited attribute hasbeen set, is stored. In a block attribute table, entries correspondingto blocks storing sections of file 1 (addresses 0000, 0002, and 0003)are set at ‘1’ indicating a write prohibited attribute. If the blockattribute table is set in this way, the write control unit 25 willreject commands to perform write processing on the blocks with addresses0000, 0002, and 0003.

FIG. 34C shows a situation when a file 2, for which a read prohibitedattribute has been set, is stored in the nonvolatile memory 1. In thiscase, a flag indicating a read prohibited attribute is set in entries inthe block attribute table that correspond to the file 2. Then, the file2 is divided into a plurality of sections, and these sections are storedin a plurality of blocks in the user area.

When the file sections of file 2 are stored in blocks with logicaladdresses 0001 and 0004, entries in the block attribute table thatcorrespond to these blocks are set at ‘2’, indicating a read prohibitedattribute. If the block attribute table is set in this way, the readcontrol unit 23 rejects commands to read data from blocks having theaddresses 0001 and 0004.

In the above embodiment, read prohibited and write prohibited attributescorresponding to each block can be set in the semiconductor memory card100, so that even if the application program 8 accesses thesemiconductor memory card 100 directly, bypassing the file systemoperation unit 9, access of files which is prohibited can be preventedby the semiconductor memory card 100. Therefore, by setting readprohibited and write prohibited attributes for blocks storing a file inthis way, protection of the file can be assured, and, should the file becopyrighted, copyright protection can also be achieved.

In this embodiment, the flag showing the write prohibited attribute isshown by ‘1’, and the flag showing the read prohibited attribute isshown by ‘2’, but these are merely examples, and the invention need notbe limited to such flags. Furthermore, in this embodiment, a blockattribute table is used to attach read and write prohibited attributesto each block in the nonvolatile memory 1, but provided that anattribute can be set for each individual block, a list or similarstructure may be used. In this embodiment, a method for setting read andwrite prohibited attributes in the nonvolatile memory 1 as blockattributes is described, but information other than that described inthe embodiments may be used as block attributes. Examples includemanaging blocks so that only users with a root privilege can obtainaccess, or giving each block a user ID, and allowing only users inpossession of that ID to obtain access, or setting access privileges toblocks for each individual user. In the above explanation of the filesystem, a FAT file system is used, but similar effects may be obtainedby using other conventional file systems such as UDF or the NewTechnology File System (NTFS) used in WindowsNT™, or a customized filesystem. Furthermore, in these embodiments, the number of sectorscontained in one erasable block is 32, but this is just one example, andthe number of sectors in one erasable block may be more or less thanthis.

Although the present invention has been fully described by way ofexamples with reference to accompanying drawings, it is to be noted thatvarious changes and modifications will be apparent to those skilled inthe art. Therefore, unless such changes and modifications depart fromthe scope of the present invention, they should be construed as beingincluded therein.

1. An access apparatus for performing file access on a semiconductormemory card that has a memory area comprising of a plurality of sectors,by managing data in each group of 2^(j) sectors (j being 0 or a positiveinteger) as a cluster, and managing one or more clusters as a file, eachgroup of 2^(i) consecutive sectors in the memory area forming a block (ibeing 0 or a positive integer), a block being a smallest unit on whichdata erasure can be performed, the access apparatus comprising: acalculation unit operable to calculate a size of volume managementinformation based on a number of clusters in the memory area that are tobe managed, the volume management information including a master bootrecord, a partition table, partition boot sector information, and a fileallocation table that indicates, for each file, links between clusterscorresponding to the file; a reserving unit operable to reserve (1) afirst area for recording the volume management information, and (2) asecond area for recording user data, the first area being formed fromblocks that are each larger in size than the calculated size of thevolume management information, and the second area being formed fromblocks following the first area; and a recording unit operable to recordvolume management information in the first area, and user data in thesecond area, wherein the recording unit operable to record the masterboot record and the partition table in a first sector of a first blockin the first area, skip a predetermined number of sectors and thenrecord the partition boot sector information and the file allocationtable, in order that a size of the first area is an integral multiple ofthe block size.
 2. The access apparatus of claim 1, wherein: thecalculation unit is operable to calculate a sum SUM by totaling a numberof sectors used to record the partition boot sector information and thefile allocation table; the first area is formed from 2^(j)×m sectors (mbeing a positive integer); the reserving unit is operable to calculatethe value of m based on {equation 1}NOM+SUM=2^(j) ×m  {equation 1} NOM being a number of sectors; and therecording unit is operable to calculate the predetermined number ofsectors by subtracting 1 from the number of sectors NOM.
 3. The accessapparatus of claim 2, wherein: the recording unit is operable to set thenumber of sectors NOM in the partition table when recording the volumemanagement information.
 4. The access apparatus of claim 2, wherein: thenumber of sectors used to record the file allocation table is based onthe number of clusters in the memory area that are to be managed.
 5. Theaccess apparatus of claim 4, wherein: the file allocation table has aplurality of entries, a number of entries corresponding to a number ofclusters recorded in the second area, and each entry showing a link toanother cluster in a same file; the access apparatus comprises: areception unit operable to receive a setting for a total number ofsectors and the number of clusters in the memory area; the calculationunit includes: a first calculation unit operable to calculate a totalnumber of clusters by dividing the total sector number by the number ofsectors 2^(j), and to calculate a size of the file allocation table bymultiplying the total number of clusters by an entry bit length, and thereserving unit includes: a second calculation unit operable to calculatea sum SUM by adding the size of the file allocation table to the numberof sectors forming the partition boot sector information, and tocalculate the value of m by substituting the sum SUM into {equation 1}.6. The access apparatus of claim 5, wherein: the memory area includes aprotected area that can only be accessed by a device connected to thesemiconductor card once an authenticity of the connected device has beenverified, and a user data area that can be accessed by the connecteddevice regardless of whether or not the authenticity of the connecteddevice has been verified; the reception unit is operable to receive,from a source outside of the access apparatus, settings for numbers ofsectors and numbers of clusters to be allocated to each of the protectedarea and the user data area; the first calculation unit is operable tocalculate a size of a file allocation table for each of the protectedarea and the user data area, based on the received settings; and thesecond calculation unit is operable to calculate two sums SUM for eachof the protected area and the user data area respectively by adding thesize of the file allocation table to the number of sectors forming thepartition boot sector information, and to calculate the value of m foreach of the protected area and the user data area by substituting eachof the two sums SUM into {equation 1}.
 7. The access apparatus of claim6, wherein: the protected area and the user data area have differentnumbers of clusters.
 8. The access apparatus of claim 5, wherein therecording unit is operable to perform: (a) first processing forrecording user data divided into a plurality of sections into the secondarea as a plurality of clusters, each section being stored in one of theplurality of clusters in the second area; (b) second processing forsetting a plurality of entries in the file allocation table, each entryshowing a link between clusters; and (c) third processing for recordinga file name and location information showing a location of a firstcluster in the file into the root directory entry.
 9. The accessapparatus of claim 8, wherein part of the file name is recorded in partof the user data area.
 10. A recording medium storing a program in acomputer-readable format for causing a computer to perform file accesson a semiconductor memory card that has a memory area comprising of aplurality of sectors, by managing data in each group of 2^(j) sectors (jbeing 0 or a positive integer) as a cluster, and managing one or moreclusters as a file, each group of 2^(i) consecutive sectors in thememory area forming a block (i being 0 or a positive integer), a blockbeing a smallest unit on which data erasure can be performed, therecording medium having the computer perform the following steps of:calculating a size of volume management information based on a number ofclusters in the memory area that are to be managed, the volumemanagement information including a master boot record, a partitiontable, partition boot sector information, and a file allocation tablethat indicates, for each file, links between clusters corresponding tothe file; reserving (1) a first area for recording the volume managementinformation, and (2) a second area for recording user data, the firstarea being formed from blocks that are each larger in size than thecalculated size of the volume management information, and the secondarea being formed from blocks following the first area; and recordingvolume management information in the first area, and user data in thesecond area, wherein the recording step records the master boot recordand the partition table in a first sector of a first block in the firstarea, skips a predetermined number of sectors and then records thepartition boot sector information and the file allocation table, inorder that a size of the first area is an integral multiple of the blocksize.
 11. The recording medium of claim 10, wherein: the calculatingstep calculates a sum SUM by totaling a number of sectors used to recordthe partition boot sector information and the file allocation table; thefirst area is formed from 2^(j)×m sectors (m being a positive integer);the reserving step calculates the value of m based on {equation 1}NOM+SUM=2^(j) ×m,  {equation 1} NOM being a number of sectors; and therecording step calculates the predetermined number of sectors bysubtracting 1 from the number of sectors NOM.
 12. The recording mediumof claim 11, wherein: the recording step sets the number of sectors NOMin the partition table when recording the volume management information.13. The recording medium of claim 12, wherein: the number of sectorsused to record the file allocation table is based on the number ofclusters in the memory area that are to be managed.
 14. The recordingmedium of claim 13, wherein: the file allocation table has a pluralityof entries, a number of entries corresponding to a number of clustersrecorded in the second area, and each entry showing a link to anothercluster in a same file; the program comprises the step of: receiving asetting for a total number of sectors and the number of clusters in thememory area; the calculating step includes the first sub-step of:calculating a total number of clusters by dividing the total sectornumber by the number of sectors 2^(j), and calculating a size of thefile allocation table by multiplying the total number of clusters by anentry bit length, and the reserving step includes the second sub-stepof: calculating a sum SUM by adding the size of the file allocationtable to the number of sectors forming the partition boot sectorinformation, and calculating the value of m by substituting the sum SUMinto {equation 1}.
 15. The recording medium of claim 14, wherein: thememory area includes a protected area that can only be accessed by adevice connected to the semiconductor card once an authenticity of theconnected device has been verified, and a user data area that can beaccessed by the connected device regardless of whether or not theauthenticity of the connected device has been verified; the receivingstep receives, from a source outside of the access apparatus, settingsfor numbers of sectors and numbers of clusters to be allocated to eachof the protected area and the user data area; the first sub-stepcalculates a size of a file allocation table for each of the protectedarea and the user data area, based on the received settings; and thesecond sub-step calculates two sums SUM for each of the protected areaand the user data area respectively by adding the size of the fileallocation table to the number of sectors forming the partition bootsector information, and calculates the value of m for each of theprotected area and the user data area by substituting each of the twosums SUM into {equation 1}.
 16. The recording medium of claim 15,wherein: the protected area and the user data area have differentnumbers of clusters.
 17. An initialization method for initializing acomputer to perform file access on a semiconductor memory card that hasa memory area comprising of a plurality of sectors, by managing data ineach group of 2^(j) sectors (j being 0 or a positive integer) as acluster, and managing one or more clusters as a file, each group of2^(i) consecutive sectors in the memory area forming a block (i being 0or a positive integer), a block being a smallest unit on which dataerasure can be performed, the initialization method comprising the stepsof: calculating a size of volume management information based on anumber of clusters in the memory area that are to be managed, the volumemanagement information including a master boot record, a partitiontable, partition boot sector information, and a file allocation tablethat indicates, for each file, links between clusters corresponding tothe file; reserving (1) a first area for recording the volume managementinformation, and (2) a second area for recording user data, the firstarea being formed from blocks that are each larger in size than thecalculated size of the volume management information, and the secondarea being formed from blocks following the first area; and recordingvolume management information in the first area, and user data in thesecond area, wherein the recording step records the master boot recordand the partition table in a first sector of a first block in the firstarea, skips a predetermined number of sectors and then records thepartition boot sector information and the file allocation table, inorder that a size of the first area is an integral multiple of the blocksize.
 18. A semiconductor memory card that has a memory area comprisingof a plurality of sectors, by managing data in each group of 2^(j)sectors (j being 0 or a positive integer) as a cluster, and managing oneor more clusters as a file, each group of 2^(i) consecutive sectors inthe memory area forming a block (i being 0 or a positive integer), ablock being a smallest unit on which data erasure can be performed, thesemiconductor memory card comprising: a first area for recording volumemanagement information; and a second area, being formed from sectorsfollowing the first area, for recording user data; the volume managementinformation including a master boot record, a partition table, partitionboot sector information, and a file allocation table that indicates, foreach file, links between clusters corresponding to the file, the masterboot record and the partition table are recorded in a first sector of afirst block in the first area, a predetermined number of sectors areskipped, and then the partition boot sector information and the fileallocation table are recorded in subsequent sectors in order that a sizeof the first area is an integral multiple of the block size.
 19. Asemiconductor memory card having a memory area that includes (1) aprotected area that can only be accessed by a device connected to thesemiconductor card once an authenticity of the connected device has beenverified, and (2) a user data area that can be accessed by the connecteddevice regardless of whether or not the authenticity of the connecteddevice has been verified, the protected area and the user data areaincluding a plurality of sectors, and managing data in each group of2^(j) sectors (j being 0 or a positive integer) as a cluster, and one ormore clusters as a file, each group of 2^(i) consecutive sectors forminga block (i being 0 or a positive integer), a block being a smallest uniton which data erasure can be performed, and at least one of theprotected area and the user data area including: a first area forrecording volume management information; and a second area, being formedfrom sectors following the first area, for recording user data; thevolume management information including a master boot record, apartition table, partition boot sector information, and a fileallocation table that indicates, for each file, links between clusterscorresponding to the file, the master boot record and the partitiontable are recorded in a first sector of a first block in the first area,a predetermined number of sectors are skipped, and then the partitionboot sector information and the file allocation table are recorded insubsequent sectors in order that a size of the first area is an integralmultiple of the block size.